1. Field of the Invention
The present invention relates to a compressor and more particularly to a compressor in which oscillating pistons reciprocate due to the rotation of a cam surfaced plate secured around a drive shaft.
2. Description of the Related Art
In compressors having double-headed pistons that reciprocate in associated cylinder bores by the rotating action of a swash plate, each piston reciprocates only once for each complete revolution the swash plate makes. One way to increase the compressor's compression displacement per rotation of the swash plate, is to design larger sized compressors. Since compressors are often mounted in vehicles, however, their large design is distinctly undesirable.
One proposed solution to the above shortcoming is the recently developed wave plate type compressor disclosed in Japanese Unexamined Patent Publication No. 57-110783. In this compressor, the swash plate is replaced with a plate having the shape of a solid cam. This cam is a disk-shaped plate having circumferentally extending undulating surfaces formed on the plate. If the wave plate has two undulations i.e., two crests and two troughs, each double-headed piston performs two compressing actions for each turn the wave plate makes. It is therefore possible to increase the compression displacement without enlarging the compressor.
To manufacture the wave shaped dish of this type of compressor, the dish must be formed with undulations in the circumferential direction, and its wavy cam surfaces should be polished. It is very difficult, however, to form and polish the undulated surfaces with any high degree of precision. Consequently, the manufacture of such a compressor containing these types of plates has proven quite difficult.
Since the crest and trough of the undulated cam surface have inverse curvatures, it is as yet not possible to form cam followers having shapes that accurately correspond to the crests and troughs of the undulated cam surface. The type of surface contact shared between the cam surface and the cam follower is a point or line contact, rather than a plane contact. This construction precludes there being any large or significant amount of contact area shared between the cam surface and the cam follower. Consequently, both cam surface and follower are subject to a large contact pressure per unit area. Such pressure tends to cause the premature wearing of the cam surface and cam follower, and thus decreases the longevity and effective service life of the compressor. This premature wearing also tends to facilitate the generation of vibration and noise in the compressor during its operation, degrading the overall smooth operation and operating environment of the compressor.